Method and apparatus for cleaning xerographic plates



8, 1969 R. H. EI'CHORN ETAL 3,424,615

METHOD AND APPARATUS FOR CLEANING XEROGRAPHIC PLATES Filed Jan. 3, 1966 Sheet I N VENTORS v ROGER H. EICHORN ORBETT H. KAUPP BY M ,4 r ra /vs s Jan. 28, 1969 R. H. EICHORN ETAL 3,424,615

METHOD AND APPARATUS FOR CLEANING XER OGRAPHIC PLATES Fi ld Jan. :5. 1966 1 Sheet lNV ENTORS ROGER H. EICHORN NORBETT H. KAUPP ,4 r romvers NbH United States Patent Claims This invention relates to xerography and, in particular, to a method and apparatus for cleaning xerographic plates. More specifically, the invention relates to a xerographic cleaning system in which granular particles are impinged against the photoconductive plate to triboelectrically remove residual powder.

The process of forming an electrostatic image on an insulating surface, as disclosed by C. F. Carlson in his US. Patent No. 2,297,691, is in wide commercial use today. This process, known as xerography, makes use of the unique properties of a xerographic or electrophotographic plate. The xerographic plate comprises a photoconductive insulating layer placed on a backing of electrically conductive material. Reusable xerographic plates are described in greater detail in US. Patent No. 2,753,278 to W. E. Bixby et al., and US. Patent No. 2,803,542 to O. Ullrich. In the xerographic process the plate is first electrostatically charged and then exposed to the image of light and shadow to be reproduced whereby the electrostatic charge on the plate is selectively dissipated to produce an electrostatic image which corresponds to the pattern of light and shadow of the original image.

The electrostatic image is made visible by placing in contact with the insulating surface an electroscopic powder; the electroscopic powder, having a charge opposite that placed on the electrophotographic plate, which will be attracted to the electrostatic image thereby rendering the image visible. The resulting powder image may be either permanently afiixed in place or may be transferred to a final image support member, such as paper or the like, and bonded thereto. Affixing the image to the support member may be done in a variety of ways depending on the nature of the electroscopic powder.

The usual method of applying the developer to an electrostatic image is to use a finely divided material called toner which is held to a larger, more coarsely divided material, called carrier. This two component developer uses the carrier to charge the toner by contact electrification, also called triboelectrification. When two initially neutral bodies are in the same locality, electrical charge will tend contact. The direction of charge transfer depends upon the A relative positions of the material on the triboelectric scale. The magnitude of charging is generally determined by the degree of separation in the triboelectric series of the two materials selected, but there are factors as yet unexplained which oifset this generalization. As a toned carrier particle passes over a charged area of the plate the electrostatic charge on the plate is sufiicient to attract the toner particle from the carrier to the plate and thus develop the electrostatic image.

It should be noted at this point that in certain xerographic processes an expendable electrophotographic plate is employed. An example of such a process is the use of a zinc oxide binder placed upon a substrate of paper to form a xerographic plate. The steps of charging, exposing, developing and fusing are performed on the specially treated support material without need to transfer the developed image. In the expendable process there is no need for a cleaning operation, therefore, it should be clear that this invention is limited to a xerographic process utilizing a reusable plate.

The developed electrostatic image is generally transferred to a support material and the electrophotographic plate prepared for reuse. The transfer operation is not efiicient so there remains on the initial image-bearing surface a residual deposit of electroscopic powder. Before reuse, the surface of the electrophotographic plate must be cleaned of this residual toner to insure good reproduction on the next cycle. Residual deposits may be left on the electrophotographic plate for other reasons. First, the statistical spread in triboelectric charging of toner particles is frequently so great that occasionally particles are charged to a polarity opposite to the polarity desired. These oppositely charged particles of toner will be deposited in the background area, therefore, when the imaged toner is electrostatically transferred to the support material, the wrongly charged toner will be rejected leaving behind undesired residue. Secondly, the threshold forces holding the transfer toner to the support material are sometimes so low that the purely mechanical action of removing the support material from the electrostatic plate will be enough to allow the toner particle to gravitate back to the plate.

Copely, in his US. Patent 2,484,782, teaches a method of removing residual toner from an electrophotographic plate by flowing granular material across an electrophotographic plate; the granules attract toner by what was then referred to as the phenomenon of electrical attraction, known today as the triboelectric effect. Such method for cleaning a plate has never been commercially utilized in rapid or automatic machines because the life of the cleaning granule is short, that is, the granule becomes saturated with toner after a few hundred cycles and must then be replaced. It has also been found that an apparatus depending on gravity for the rate of cleaner flow is severely limited as to speed of machine operation.

Fur brush cleaners which are rotated against the surface of the xerographic drum, as disclosed in Walkup Patent No. 2,832,977, have worked well, however, such brush materials possessing the properties needed to remove residual toner from the plate are expensive and have a relatively short life. Brush cleaning systems usually employ a vacuum and filter system to remove the residual powder from the machine further adding to the cost and size of such systems.

A disposable web of fibrous material, placed in contact with the plate, is sometimes used to rub or wipe residual toner from the plate. Graff, in his US. Patent No. 3,186,- 838, described such a web cleaner employed in a xerographic process. Web cleaning has an advantage over brush cleaning in that it presents a new and unused rubbing surface to the xerographic plate during each cleaning cycle. However, as the speed of xerographic machines increase so must the size of the web used. The apparatus used in a high speed machine to store and advance the web, as well as to rub or wipe the plate clean, :must, by its very nature, he bulky. Heretofore, apparatus used to clean electrophotographic plates in xerographic machines have employed cleaners which are placed in rubbing contact with the photoconductive surface of the plate. In high speed machines, rubbing surfaces quickly become saturated with the residual developing powder removed from the plate. This invention contemplates cleaning xerographic plates with a material which will attract powder from the plate and give up the powder to another body so that the cleaning material can be reused.

It is therefore an object of this invention to clean xerographic plates.

It is also an object of this invention to improve apparatus for cleaning Xerographic plates.

A further object of this invention is to clean a xerographic plate by triboelectrically attracting residual powder from the plate.

It is a further object of this invention to improve xerographic cleaning apparatus so that the cleaning material can be reclaimed for reuse without removing the cleaning material from the apparatus.

And it is a further object of this invention to increase the efficiency of Xerographic cleaning operation by regenerating the cleaning material for reuse.

These and other objects of this invention are attained by means of an impeller wheel extending into a reservoir holding granule particles having triboelectric properties such that the granule will attract residual developing powder when brought into close proximity or contact with the developing powder. As the impeller is rotated granules from the reservoir are impinged against a Xerographic plate having residual developing powder upon it. The cleaning granules, after attracting the residual powder from the plate, continue to move towards and are intercepted by a biased grid. The grid is biased at a potential sufficient enough to remove the residual powder from the cleaning granule, the granule then being returned to the reservoir where it can be reused.

For a better understanding of the invention as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings wherein:

FIG. 1 is a schematic side sectional view of a Xerographic machine embodying the invention;

FIG. 2 is a sectional view through the cleaning unit of the machine shown in FIG. 1;

FIG. 3 is an embodiment of the cleaning unit having a plurality of paddle wheels;

FIG. 4 is a section through the grid showing its construction.

For a general understanding of the process of electrophotography in which this cleaning system is utilized, reference is had to FIG. 1 which shows the paddle wheel cleaner embodied in an automatic Xerographic machine. In the Xerographic process, a light image is projected onto an electrophotographic plate which previously has had a uniform charge placed upon it; the variation in light intensity producing an electrostatic or latent image upon the plate surface. The latent image is developed by a tribeelectrically charged developing material which deposits powder in the areas corresponding to the latent image. The image is then electrostatically transferred to a support material where it is permanently fused. The plate surface is cleaned and prepared for the next cycle.

In the Xerographic process as shown in FIG. 1, opque copy 9 is placed in support tray 10 from which it is fed onto transport means 11 which is driven by motor 12. The speed of the transport means, in this case an endless belt, is synchronized with the speed of the Xerographic plate mounted on drum 20 whereby the peripheral rate of the drum surface is identical to the rate of movement of the reflected light image. The copy is moved past the optical axis of lens system 13 where it is illuminated by lamp LMP-1 causing a light image of the original to pass through adjustable lens 14 upward through variable aperture slit 15 onto the Xerographic plate.

Xerographic drum 20 includes a cylindrical drive member mounted in suitable bearings in the frame of the machine; said drive member being driven in a counterclockwise direction, as shown, by motor 22. The drum surface comprises a layer of photoconductive material mounted on a conductive backing, the sensitized layer being electrostatically charged prior to exposure by means of a corona generating device 23, similar to the type disclosed in Walkup Patent No. 2,777,957. The corona generating device energizes the Xerographic plate to a sufficiently high potential so that the developing pattern will be attracted to the plate.

The exposure of the energized plate to the light reflected from the original copy will discharge the photoconductive layer in the area struck by light, thereby causing a latent electrostatic image to remain on the drum. This latent electrostatic image is passed through developing station 25 in which two-component developing material 26 is impinged against the drum. The two-component developing material, as disclosed in Walkup Patent No. 2,638,416, gives up its developing powder or toner from carrier granule to electrophotographic plate 20 because the electrostatic attraction between toner and plate is greater than between toner and carrier granule.

In the developing apparatus, two-component developing material is deposited in the sump area of housing 29. The conveyor with paddles 30 attached, is driven by motor 28 in a rotary manner during operation of the apparatus but any suitable drive system capable of rotating conveyor at a desired speed may be utilized. Buckets 30, on the conveyor, extend into the sump containing the developer material so that rotation of the conveyor, in the direction indicated, will lift developer material from the reservoir and deliver it to the surface of the Xerographic drum where the developing powder is electrostatically attracted to the charge image area.

The developed latent image then moves through discharge station 40 where lamp LMP-Z floods the developed electrophotographic plate with light removing any charge which may have been left in the non-image areas. Thereafter, the developed latent image is passed to transfer station 33 at which point the charged powder image is electrostatically transferred to support surface 34. In the particular embodiment shown in FIG. 1, support surface 34 is a paper web, but any convenient type of material may be used. The web is supplied by roll 35 and fed over guide rolls 36 and 37 which hold the support material in contact with the image bearing drum. The support material is moved at the same peripheral speed as the Xerographic drum and, at the same time, the image is electrostatically transferred from the plate to the support material. A second corona generating device 41 places a charge, opposite to the charge on the developing powder, necessary to attract the toner from the plate to the support material. A motor moves the support material at the same rate as the Xerographic drum, drives take-up roll 38 and its associated guide and tensioning rolls 43.

After transfer, the support surface is separated from the drum and guided through a suitable fusing means 42 whereby the developing powder is permanently aflixed to the support material. Any suitable means for bonding the developer to the support may be used.

As previously stated, some residual developing powder will remain upon the Xerographic plate after the transfer operation has been completed. This residual toner may be present for a number of reasons, first, some residual powder will mechanically bond itself to the plate; second, there is a residue of triboelectric charge on some developing powder during the transfer operation which makes electrostatic transfer of the developer impossible; and thirdly, the electrostatic transfer operation is not successful thereby leaving behind some developer in the image area. This residuum found on the plate after the transfer operation should be cleaned from the photoconductive surface before the plate is prepared for reuse in the xerographic process. Cleaning apparatus constructed in accordance with this invention, as illustrated in FIGS. 1, 2 and 3, may be adapted to any Xerographic process that requires reuse of the electrophotographic plate.

A corona generating device 51, situated adjacent to transfer station 33, applies a charge of opposite polarity to that of transfer corot-ron 41 thereby attempting to negate the electrostatic attraction between powder and plate created during transfer. It is felt that applying this opposite charge will enhance the cleaning operation.

As shown in FIGS. 1 and 2, cleaning granules 50 are stored in reservoir 49 located in the cleaner housing 47, the cleaning granules 50 possess triboelectric properties such that when they are brought in close proximity, or in actual contact, with the residual developing powder there is an exchange of charge between the two suificient enough to attract the developing powder from the xerographic plate. The granules are brought in close proximity with the developing powder on the plate by means of impeller wheel 54 which hurls the cleaning granules from the reservoir against the xerographic plate positioned in the sidewall opening of the cleaner housing 47. Impeller 54 is constructed with a plurality of paddles 57 along the outer periphery, the impeller being mounted on shaft 55 and driven through any suitable driving means capable of rotating the impeller at the desired speed. In this particular embodiment, the shaft is driven by motor 45 through belt and pulley system 46. The impeller is journaled in the housing so that paddles 57 extend into the reservoir 49. As the impeller is rotated in the direction indicated, the granules will be impinged upon the electrophotographic plate; the amount of cleaning material delivered to the plate surface being determined by the rotational speed of the impeller. The cleaning granules, although being large in comparison to the size of the developing powder, are of small enough size so that they will not scratch or mar the photoconductive surface when they are hurled or impelled against the drum. Although the impeller, as shown in this embodiment, has an individual driving means, it is quite feasible to drive the impeller in a fixed relationship with drum, utilizing a single drive means, whereby the amount of cleaning material delivered to the plate would vary wit-h the change in the speed of the xerographic drum. As can be seen, a high degree of flexibility may be obtained in selection of drum speeds utilizing this type of system.

The physical positioning of the various components within the apparatus is such that the granule, upon being impinged against the electroph-otographic plate, will continue to move towards and be intercepted by a grid 58. The grid is biased at a DC potential, of approximately 600 to 1,000 volts or to a voltage sufiicient to electrostatically attract the triboelectrically charged developed powder from the intercepted granule. The granule is free to sift through the grid and return to the reservoir while the powder is attracted and retained by the grid. The biasing potential is supplied from DC biasing source 62 through slip ring 76. To insure that the grid maintains the proper bias, it must be electrically isolated from the normally grounded apparatus, therefore, bearings 60 and driving gear 67 are constructed of non-conducting material which acts to electrically insulate the grid system. Electrical interlocks (not shown) may be provided so that when door 74 is open, or when drum 20 is removed, the electrical connection in the grid circuit is broken and the high potential is drained to ground thereby insuring the safety of anyone working in this area.

Referring now to FIG. 4, grid 58 is constructed of a conductive mesh of fiber-like material 85, such as steel wool. In the embodiment shown in FIGS. 1 and 2 the grid is in the shape of a cylinder. The density of the fiber-like mesh being greater along the axial center line of the cylinder and decreasing proportionally toward the extremities. The density of the mesh is such as to allow a cleaning granule to penetrate beyond the outer surface of the grid thereby utilizing as much of the mesh-like area as possible. The granule, upon giving up the residual developing powder to the grid, filters through the mesh and is free to fall back into the housing reservoir. To further utilize all of the grids mesh-like surface area, the grid is rotatably mounted upon shaft 64 so that periodically a fresh surface may be presented to the impelled cleaning granules leaving the plate. Motor 66 is electrically connected to an electrical counting device (not shown) so as to rotate the grid a predetermined number of degrees for any desired number of cleaning cycles. As shown in FIG. 2, a pinion 70, mounted on the shaft of motor 66, drives nonconducting gear 67 the desired number of degrees, however, any suitable means capable of rotating the grid can be employed.

Grid 58 is affixed to shaft '64 and is adapted to be replaced in the apparatus when the grid becomes contaminated with residual developing powder. Shaft 64 is mated to a female member in drive shaft 71. The opposite end of shaft 64 has a hollow section provided to receive paper support member 73. To remove grid unit 58 from the apparatus housing, door 74, which is provided with an electrical interlock, is placed in the open position thus moving support member 73 from its normal supporting and locating position. Shank 72, machined on shaft 64, and it female receiving member in drive shaft 71 are of sufficient length to support the replaceable grid unit in cantilever fashion when support member 73 is removed. The unit is removed by sliding it free of drive shaft T1, in through the opening provided in the housing. A new unit, after being mated to shaft 71, is properl relocated by closing door 74 which reposition support member 73 in the hollow section of shaft 64.

It has been found that an uncontaminated cleaning granule, that is one which has no residual powder triboelectrically adhering to it, displays a tendency to triboelectrically bond itself to the xerographic plate. The granule will remain on the plate until it is physically removed which sometimes results in scratching or scarring of the plate. The cleaning system described herein will deliver to the reservoir from the grid a granule with a contamination of between 0.3% to 1.0%, that is, with 0.3% to 1.0% of the total toner it can triboelectrically hold. This contamination is well within an acceptable range for eflicient operation of such cleaning apparatus.

If for some reason, such as a space limitation or the like, a rotatable grid is not desired or is not feasible, a configuration as shown in FIG. 3 may 'be utilized. In this embodiment, two counter-rotating impellers hurl the cleaning granules against a single biased .grid. Rectangular shaped grid is placed between impeller wheels 81 and 82 in such a manner that the intercepted granules strike either side of the grid thus utilizing the exposed surface area to attract and hold residual cleaning powder. Impeller 81, rotating in the direction shown, performs a first cleaning operation upon the xerographic plate while impeller 82, rotating in the opposite direction, performs a second cleaning operation. This embodiment, employing a plurality of counter-rotating impellers to give a series of cleanings, is particularly suited for use in high speed machines. The plurality of impellers, although not consuming a great amount of space, are capable of delivering a large amount of cleaning material in a short period of time.

While the invention has been described with reference to the structure disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purpose of the improvements or the scope of the following claims.

What is claimed is:

1. Apparatus for cleaning residual developing powder from an electrophoto-graphic plate by granule particles having triboelectric properties sufiicient to attract said powder from the plate, such apparatus including a housing with a reservoir capable of holding a quantity of said granules,

the housing having an opening adapted to receive an electrophotographic member,

means to place the granular cleaning particles in close proximity to the residual developing powder on said electrophotographic member so that the powder will be attracted from the electrophotographic member to the cleaning granule, and

means to separate the residual powder from said cleaning granule.

2. Cleaning apparatus according to claim 1 in which said member to separate the residual powder from the granule comprises an electrically insulated grid of potential suflicient to electrostatically attract the residual developing powder from the cleaning granule to said grid.

3. Apparatus according to claim .1 in which means to place the granule cleaning particle in close proximity to the residual developing powder on the electrophotographic member comprises an impeller, journaled in the housing, to impinge the cleaning granule against the electrophotographic member positioned in the housing opening where said granules attract powder from said electrophotographic member.

4. Apparatus according to claim 3 wherein said impeller journaled in the housing has a plurality of blades extending into said reservoir, said impeller being driven rotatably so that the granules from the reservoir are impinged against the electrophotographic member in the housing opening, and further means to separate the residual developing powder from said cleaning granule comprises an electrically insulated grid, biased to a potential suflicient to attract residual powder from the impelled cleaning granule striking said grid.

5. Apparatus for removing residual developing powder from an electrophotographic member by triboelectrically attracting said powder from the member to a granular cleaning particle placed in close proximity to the developing powder, such apparatus including a housing with a reservoir capable of holding a quantity of cleaning granules,

the housing having an opening adapted to receive an electrophotographic member,

an impeller, journaled in the housing, upon which is mounted a plurality of blades extending into the reservoir, means to drive the impeller rotatably so that the granules from the reservoir are impinged against an electrophotographic member in the housing opening,

an electrically insulated grid positioned to intercept the impinged granules leaving the electrophotographic member, and

a biasing means to place a suflicient potential on said grid to attract residual developing powder from the impelled cleaning granules, said granules returning to the reservoir.

6. Apparatus in accordance with claim 5 in which the grid is constructed of a conducted mesh of fiber-like material providing a surface area capable of retaining a quantity of attracted residual developing powder.

7. Apparatus according to claim 5 in which the grid is constructed of a conductive mesh of fiber-like material providing sufficient surface area to retain a quantity of residual powder, said grid constructed in the shape of a cylinder, the density of the fiberlike material being greatest along the axial center line of the cylinder and becoming proportionally less towards the extremities so that an intercepted cleaning granule will penetrate the outer surface or the cylinder thereby utilizing the internal mesh surface to retain attracted residual developing powder. 8. A cleaning apparatus according to claim 7 wherein the grid is rotatably mounted in a housing and having means to periodically adjust the grid to present a new surface area to the cleaning granules.

9. The cleaning apparatus according to claim 5 wherein the impeller consists of counter-rotating members and wherein the grid is constructed of a conductive mesh of fiber-like material, is rectangular in shape, and is positioned between the counter rotating members so that the impinged cleaning granules leaving the electrophotographic member are intercepted on opposing sides of the grid. 10. A method of removing residual developing powder from an electrophotographic member comprising propelling a granule particle having triboelectric properties sufficient to attract residual powder against an electrophotographic plate so that said granules are placed in contact with said residual powder,

interrupting the flight of the propelled cleaning granules leaving the electrophotographic member with an electrically insulated conductive grid,

separating the residual powder triboelectrically held to said granules by electrically attracting said powder from the granules to said grid,

collecting the regenerated cleaning granules for reuse in the cleaning process.

References Cited UNITED STATES PATENTS 6/1956 Walkup et al. l34l 12/1960 Vyverberg 1341 X US. Cl. X.R. 1341 

10. A METHOD OF REMOVING RESIDUAL DEVELOPING POWDER FROM AN ELECTROPHOTOGRAPHIC MEMBER COMPRISING PROPELLING A GRANULE PARTICLE HAVING TRIBOELECTRIC PROPERTIES SUFFICIENT TO ATTRACT RESIDUAL POWDER AGAINST AN ELECTROPHOTOGRAPHIC PLATE SO THAT SAID GRANULES ARE PLACED IN CONTACT WITH SAID RESIDUAL POWDER, INTERRUPTING THE FLIGHT OF THE PROPELLED CLEANING GRANULES LEAVING THE ELECTROPHOTOGRAPHIC MEMBER WITH AN ELECTRICALLY INSULATED CONDUCTIVE GRID, 